Rotary winged aircraft



y 1, 1940. H. s. CAMPBELL 2,201,810

' ROTARY WINGED AIRCRAFT Filed March 7, 1938 2 Sheets-Sheet 1 OFF CLUTCH0N INVENT OR.

M 4. W BY A1TORNEYS y 1, 1940. H. s. CAMPBELL 2,201,810

ROTARY WINGED AIRCRAFT Filed March 7, -193a 2 Sheets-Sheet 2 1 i I /0 ii 1 B 1- V M 2 I a l 1 J 4 1 g ROTATION 1 4: t ROTATION 74 069 E l 7/ 4INVENTOR.

' ATTORNEYS.

lated to a generally upright hub. initial thrust is obtained fortake-oi! purposes. I Still more specifically, the invention 'hasref- Thestructural features further provide for deerence to a blade mountingproviding for. pitch crease of blade pitch to the normal autorotachangemovements under different conditions of tional rate upon reduction ofrotor speed to the operation. substantially normal autorotational rate.

The invention contemplates a blade mounting Still further, the inventionhas in view proto such as to provide for automatic change of bladevision of locking means, serving primarily as a pitch in one sense uponapplication of driving safety device, for ensuring that the blade willtorque to the rotor, centrifugal force preferably retain the desiredpitch setting for diflerent conbeing relied upon to effect pitch changemoveditions, even when unintentional momentary rement in the oppositesense upon cessation of the duction in driving torque occurs. In thepredriving torque ferred embodiment the locking means is inter- Stillmore particularly, the invention provides locked with the control forthe rotor driving pivot mechanism for mounting the blade or bladesmeans, as will appear more my hereinafter. 1 of the rotor, preferablyincluding a pitch change The manner in which the foregoing objectshinge, arranged to provide decrease of blade and advantages are attainedwill appear to best pitch upon application. of a driving torque andadvantage from a consideration of the following increase of blade pitchunder the influence of description referring to the accompanyingdrawcentrifugal force upon cessation of the driving ings, in whicht0rqueFigure l is a somewhat diagrammatic side view Still another object ofthe invention is to proof a rotor head, the root end of two blades, arovide a plurality of mounting pivots for each tor drive mechanism, andcontrol system thereblade, including a "flapping pivot to, compensatefor, all constructed in accordance with the infor difierential liftefiects, a drag" pivot to provention, and certain parts being shown invervide freedom for lag and lead displacements of tical section; theblade under the influence of flight forces, Figure 2 is a view taken asindicated by the and the oblique pitch change pivot already menline 2-2on Figure 1, the view being on an entioned, all of the pivots and theblade pitch set-- larged scale and certain parts of the locking tingbeing such as to provide for autorotational 'means shown in section; andactuation of the motor in flight, and the drag Figure 3 is a viewsimilar to Figure 2 but illusand pitch change pivots being arranged toprotrating a modified construction. T vide for lag and leaddisplacements of the blade Referring to Figure l, a rotative hub orspindle during autorotational actuation about the drag is shown at 4,this hub part having pairs of aperhinge only, the oblique pitch changepivot at this tured ears 5 to which the blades of the rotor time beingrendered inoperative under the inare connected by means of substantiallyhorifluence of flight forces but being capable of being zontal orflapping pivots 6. The rotor may in- 40 brought into operation when adriving torque is corporate any desired number of blades, the formapplied to the rotor. Such driving torque may shown including three suchblades, the inner desirably be delivered to the rotor for purposes endsof two of which appear at I. The structure of starting the rotor oroverspeeding" the rotor of each blade is built up on a main spar 8having prior to take-off from the ground, so as to effect at its innerend a forked fitting 9 cooperating steep or substantially verticaltake-oil without with another fork member In, these two memtorque in thebody of the craft, by cutting of! hers being joined by a drag pivot llpositioned the drive prior to the time the machine actually to providefreedom for lag and lead movements leaves the ground, this general styleof flight of the blade substantially generally in its path beingdisclosed more fullyinthe copending appliof rotation. A damper device l2may be arcation of Juan de la Cierva, Serial No. 738,349, ranged betweenthe pairs of prongs of the fork filed August 3, 1934. members 9 and ID,as shown for example in the In accordance with another aspect of theincopending application of Agnew E. Larsen, 'Sevention, provision ismade for automatically carrial No. 106,343, filed October 19, 1936, nowPat- Patented May 21, 1 940 r UNITED (STATES PATENT OFFICE 2,201,810ROTARY 'wrNGan AIRCRAFT Harris S. Campbell, Willow Grove, Pa., asoignor,by mesne assignments, to Autogiro Company oi America, a corporation ofDelaware 'Appllcation March I, 1938, Serial No. 194,288

19 Claims. (Cl. 244-18) This invention relates to rotary winged aircraftand especially to that general type of craft which is equipped with abladed sustaining rotor in which the blade or blades of the rotor arearticurying the blade pitch movement about the oblique pitch changepivot to a higher than normal autorotational setting upon cutting oil ofthe drive at a rotational rate higher than the normal autorotationalrate, whereby a highdegree of cut No. 2,155,427, dated April 25, 1939.This damper device may serve to control or restrict blade movementsabout the drag pivot II in flight operation.

The member or link I extended inwardly fromthe drag pivot is provided atits inner end with opposed bearing housings l3-l3 for mounting rollerbearings ll which cooperate with the oblique pitch change pivot l5,which pivot also cooperates with a second link l3 which is apertured atits inner end for cooperation with the flapping pivot 8. Each blade isthus mounted for pivotal movement in a direction generally transverseits rotative path of travel (about the flapping pivot 6), for pivotalmovement within the path of rotation (about the drag pivot H) and forpitch change movement (upon lag and lead displacements about the obliquepivot IS).

The rotative hub part 4 is journalled as by one or more bearings I1within a non-rotative hub casing 18 which is preferably mounted within agimbal ring 19 by means of a pair of trunnions 2020. The gimbal ring inturn is carried on any suitable fixed rotor support by means oftrunnions 2|. In this way freedom is provided for tilting movement ofthe entire rotor hub assembly in all directions, such tilting being ofuse for purposes of control of the craft in flight, in the mannerdisclosed in copending application of Juan de la Cierva, Serial No.645,985, filed December 6, 1932.

Toward its lower end, and within the housing 22, the rotative hub part 4is provided with a gear 23 cooperating with pinion 24 mounted at theupper end of drive shaft 25. Torque may thus be delivered to the rotor,and it may here be noted that provision is preferably made for freeoverrunning of the rotor with respect to the drive, as by means of anoverrunm'ng clutch associated with the ring gear 23.

The lower end of drive shaft 25 is geared as at 28--2'I to shaft 28,connected with the delivery side of a clutch device 29, the driving sidethereof being associated with the power shaft 30 which preferably iscoupled to the forward propulsion engine (not shown) for the craft. Theclutch and gearing parts just mentioned may conveniently be housedwithin a casing 3!, out of which the clutch actuating shaft 32 projectsfor connection with the actuating arm 33. The clutch may be actuated bymeans of a cable 34 extended for connection to the manually actuablecontrol organ 35, the clutch being biased to release position by spring36.

Any suitable flexible joints 3'! may be inserted in the drive shafting25 to-accommodate tilting movement of the rotor hub.

Turning again to the blade pivot arrangement, it is here noted that theemployment of a triple articulation mounting for a blade, incorporatinga flapping, a drag, and a pitch change pivot, is not per se a part ofthe present invention, the same being described and claimed in copendingapplication of J. A. J. Bennett, Serial No. 21,454, filed May 14, 1935,now Patent No. 2,154,601, dated April 18, 1939. Certain'improvedarrangements of these pivots, and associated mechanisms, control devicesand the like, however, as described hereinafter, perform some desirablenew functions and effect improvements in operation. In consideringthese, reference is now made to Figure 2. As here shown, the axis of thepitch change pivot I5 is offset forwardly (with respect to the directionof rotation of the rotor) from the longitudinal axis of the blade, orfrom a line A-A joining the center of gravity of the blade with the axisof the hub indicated at B. Because of this offset, it will be seen thatunder the influence of centrifugal force, a moment is set up tending tomove the blade on the pitch change pivot I! in a leading direction. Theapplication of a driving torque to the rotor hub 4, however, tends tocause the blade to lag on the axis of pivot l5, and the inventioncontemplates so locating the axis of this pivot as to obtain automaticlag and lead movements about pivot I! as between "power on" and "poweroff" conditions. In association with this offset, deflnite limits ofmovement are established by means of stop devices constructed asfollows:

A pair of upper and lower spaced arms 38 project rearwardly from, thebearing housings I3 for the pitch pivot (with respect to the directionof rotation), these arms being bridged at their outer ends by an arcuatemember 39 having stops 40 and 4| toward opposite ends thereof. The linkmember l6 carries a similarly projecting arm 42 located between the arms33 and having stop surfaces 43 and 44 adapted to cooperate respectivelywith stops 40 and H.

In low pitch position the stop surface 43 abuts stop 40, and in theautorotational pitch position (the position of Figure 2) the stopsurface 44 abuts stop 4|. The stop devices thus define a range of pitchchange movement limited, on the one hand, preferably by a substantiallyzero value for use during starting of the rotor and overspeeding fordirect take-01f and, on the other hand, by a value suitable forautorotational flight.

The position of the pivot, i. e. its offset from the center of rotationof the rotor and its offset forwardly from the line A-A, is determinedin accordance with the following.

Its distance from the center of rotation (the axis of the hub) should besuch that during application of the driving torque to the hub, thecentrifugal force on the blade, even when rotating at a substantiallyhigher than normal autorotational speed, is insuflicient to overcome orbalance the lagging effect incident to application of the drivingtorque. During application of the driving torque, therefore, the stopsurface 43 remains in engagement with stop 40. On cessation of thedriving torque, the blade moves about the pivot l5 under the influenceof the restoring moment set up by centrifugal force until the stopsurface 44 abuts the stop 4| (the position of Figure 2). The oflset ofpivot IS with respect to line AA should be sufficient to ensure positiveaction withrespect to change of blade pitch from the low to the highervalue.

In normal autorotative flight operation, therefore, lag and leadmovements of the blade in response to flight forces take place about thedrag pivot Ii, the pitch change pivot remaining ineffective. To ensurethat this condition will prevail, the forward offset of the pitch pivotl5 should be suflicient so that even with maximum leading displacementsof the blade about the drag pivot H, a line joining the center ofgravity of the blade and the hub axis will lie behind the axis of pivotl5. Unless the foregoing condition exists there would be an undesirablereverse moment about the pitch pivot i5, which condition would befurther aggravated by the action of the blade damper device H.

The two offsets of the pitch pivot l5 (offset from the center ofrotation and offset from the blade axis) are, of course, related to eachother in the sense that different values for one offset will requiredifferent values for the other.

' In accordance with the foregoing, the invention provides a pivotalblade mounting affording freedom for pitch change movements for startinsand take-oi! purposes, and also for lag and lead movements under theinfluence of flight. forces,

the entire blade operation as to these movements being automatic in thatthe driving torque and flight forces are utilized to ensure flightmovements about the drag pivot and pitch change movements for startingand take-oi! about the pitch'change pivot.

With a view to ensuring positive retention of the desired blade positioneither in driving the rotor or in flight, a latch mechanism ispreferably employed. This latch includes a pin 45'adapted alternativelyto engage in apertures 45 and 41- formed irr the arcuate member 39.These two apertures define the zero and flight pitch positions, and whenthe pin is in. engagement with either, the blade is positively retainedin that position. The latch is urged in a direction to enter eitheraperture by means of compression spring 48 housed within a suitable boreformed in the-outer end of arm 42, which arm has a central cut-outportion 49' receiving lever 50 to which the pin is coupled as at 5|; Atone end the lever is carried by a pivot 52 supported by apertured cars53. At its other end the lever is connected to a cable 54 extendedinwardly and thence downwardly into the central hollow in the hub forattachment to ring 55 which is vertically movable in the hub butrestrained as against rotation relative to the hub by a spline 55. Inorder to avoid undesired actuation of the latching pins as a result ofupward and downward flapping movement of the blades on the pivot 5, aflexible sheath 51 is provided for the cable, this sheath being securedas by brackets 58 to the link It and also to the interior of the hub. I

Ring 55 may be moved downwardly in order to withdraw the latching pinsby means of a cable 59 to which is connected'at its upper end to aninner bearing member 50, with respect to which the ring 55 is freelyrotatable. Cable 59 may-pass over a suitable pulley SI for connectionwith arm 62 of a bell crank pivoted at 63, the other arm 64 of this bellcrank being positioned to engage a projection or cam element 65 which iscarried 'by the starter clutch actuating shaft' 35. As will be seen fromthe dotted line position of lever 64 and of the operating handle 35a.for theclutch, the lever is raised during outward movement of the clutchcontrol and then lowered again when the clutch control reaches itsoutermost position. Similar movement of lever 54 takes place upon returnmovement of the clutch control.

To-consider the operation of this mechanism, assume first that the craftis on the ground and preparation is being made to effect a take-ofl. Forthis purpose, after starting of the propulsion engine which drives shaft30, the pilot draws the clutch handle 35a outwardly, an initial portionof this movement resulting in raising of the lever 64 with the resultthat the latching pins 45 for the several blades are withdrawn from theretention of zero pitch during driving and overspeeding of the rotor.Engagement of the pins in the aperture 45 in this manner ensures thatthe desired zero pitch position will be maintained even in the event ofpartial failure of the driving torque, as a result, for example, of theengine stalling. When the desired rate of rotor rotation has beenattained, the clutch handle 35a is pushed inwardly again to the offposition, and

during this inward movement the lever 54 is raised and maintained in itsupper position until the clutch is disengaged, thus removing the torquefrom the hub and permitting the action of centrifugal force to move theblades about 'the pitch change pivots l5. Completion of the one of thebearing housings [3 for the pivot l5 is provided with radiallyprojecting stops 66 and 51 defining a range of movement limited, on theone hand (by stop 65) to a value approxi- 'mating zero pitch positionfor starting purposes as before, and, on the other hand (by stop 51) toa value substantially higher than the normal autorotational pitch. Acooperating stop device 58 is mountedon the link l6 and provided withabutment surfaces 59 and 10 adapted to cooperate respectively with stops66 and 61. This device 68 further serves to house the latching pin Hwhich is urged inwardly (to latching position) by means of the spring12. Intermediate the travel provided between the stops 66 and 61, thehousing l3 has a recess 13 into which the pin II projects, to retainthe'blade in the position of substantially normal autorotational pitch.Another recess for the latching pin is provided toward the low pitch endof the range, as at 14.

Link It further carries an arm I5 projecting inwardly therefrom over theflapping pivot 6 to cooperate with a complementary arm 16 which is rigidwith one of the bearing housings l3. These two levers (l5 and 16) 'thusmove toward and away from each other during movement of the blade aboutpivot I5. Compression springs 11 are interposed between these two leversso as to urge them away from each other. The purposes and action of theforegoing mechanism can best be understood froma description of itsoperation as given just; below, it being here pointed out that thecontrol system for the latch as shown and described in connection withFigures 1 and 2, is here also intended to be utilized.

Upon commencement of the movement of the clutch control handle 35!; fromoff toward on position, the cable 54 withdraws latching pin H againstthe pressure of spring 12. As the rotor starts turning in response toengagement of the clutch, the blade lags about pivot l5 until stopsurface 59 comes into engagement with stop 66.

.When the clutch is fully engaged, the resultant drop of lever 64 of thecontrol system permits spring 72 to advance the latch pin it intoaperture 14. This therefore positively retains the blade pitch at thedesired low value for starting and overspeedlng.

Upon releasing movement of the clutch control "a, the latch pin is firstwithdrawn and then the torque is cut on from the rotor (by disconnectionof the clutch 28), in consequence of which the action of centrifugalforce on the blade causes it to move forwardly about the pivot I5 untilthe abutment surface comes into contact with the stop 61. As a safetydevice to prevent engagement of pin II in the recess 13 during thismovement, a member 18 is pivotally mounted within recess 13 and urged bycompression spring 18 to a position in which the opening to recess 13 isat least in part blocked. Assurance is thereby provided that thelatching pin will .pass across the aperture 13 to permit the blade pitchto increase to the higher than normal autorotational value defined bythe stop 61.

The high pitch, of course, produces a high initial thrust, and when thekinetic energy stored in the rotor has been expended, the rotor slowsdown to a speed approximating the normal autorotational speed. When thisoccurs, the springs 11 urge the arms 15 and 16 away from each other, andthis results in movement of the blade about pivot I5 rearwardly withrespect to the direction of rotation. Motion in this direction, however,is arrested by engagement of the latching pin H in recess 13, thisengagement being permitted by virtue of the pivotal mounting of themember 18. The position of the parts shown in Figure 3 is that of normalflight operation when the rotor is autorotationally actuated. A latchingdevice of this general type is disclosed in my copending application147,460, filed June 10, 1937.

In connection with the spring I? and the lagging moment producedthereby, in the preferred arrangement the relation between this momentand the leading moment which is set up as a result of centrifugal force(because of the forwardly offset position of pivot I5), is such that thetwo moments substantially balance each other at a. rotational speedapproximating that of normal autorotational flight for the rotor. As therotational speed increases, the centrifugal moment also increases, andby virtue of this fact I am. enabled to obtain automatic overpitchingfor jump take-off purposes, as well as automatic return of blade pitchfrom the higher than normal value to the normal autorotational value.

As with the arrangement of Figures 1 and 2, the latching device need notnecessarily be employed, although I prefer to use it in order topositively assure maintenance of the desired pitch under all conditions.

In both of the arrangements described, provision is made for pitchchange movements about an oblique pivot for starting and take-offpurposes, and at the same time the mechanism is so worked out that underthe influence of the normal forces of flight (in the absence of torqueapplied to the rotor) lag and lead displacements of the blade take placeabout one pivot, which, in the preferred arrangement, is not accompaniedby pitch change movements, at least not to the same degree ornecessarily in the same sense as the pitch change about the obliquepivot. Stated in another way, the lag and lead movements of flightoperation are assigned to one pivot, and the lag and lead movementsincident to application and cessation .of torque are assigned to anotherpivot, the operation being automatic since the atomic torque and flightforces alone are sufiicient to maintain the desired operation on the twopivots.

Advantages are also to be attained in using the latch control devices,as a result of which, for example, stalling of the engine during drivingwill not result in change of blade pitch which might effect prematuretake-oil.

I claim:

1. In an aircraft sustaining rotor having a hub and a blade, pivot meansarticulating the blade to the hub comprising a pivot having its axisangled with respect to a plane perpendicular to the axis of the hub andpassing a line joining the center of gravity of the blade and the axisof the hub in a forwardly offset position with respect thereto when theblade is in true radial position.

2. In an aircraft sustaining rotor having a hub and a blade, pivot meansarticulating the blade to the hub comprising a pivot having its axisangled with respect to a plane perpendicular to the axis of the hub andpassing a line joining the center of gravity of the blade and the axisof the hub in a forwardly offset position with respect thereto when theblade is in true radial position, and a stop limiting leadingdisplacement of the blade about said pivot axis.

3. In an aircraft sustaining rotor having a hub and a blade, pivot meansarticulating the blade to thehub comprising a pivot having its axisangled with respect to a plane perpendicular to the axis of the hub andpassing a line joining the center of gravity of the blade and the axisof the hub in a forwardly offset position with respect thereto when theblade is in true radial position and a stop limiting leadingdisplacement of the blade about said pivot axis to a position in whichthe blade is in a truly radial position.

4. In an aircraft sustaining rotor having a hub and a blade, pivot meansfor articulating the blade to the hub including two pivots both angledwith respect to a plane perpendicular to the hub axis, the axis of oneof said pivots passing a line joining the center of gravity of the bladeand the hub axis in a forwardly offset position with respect theretowhen the blade is in true radial position.

5. In an aircraft sustaining rotor having a hub and a blade, pivot meansarticulating the blade to the hub comprising a pivot having its axisangled with respect to a plane perpendicular to the axis of the hub andpassing a line joining the center of gravity of the blade and the axisof the hub in a forwardly offset position with respect thereto when theblade is in true radial position, and a stop limiting leadingdisplacement of the blade about said pivot axis, the position of thepivot axis and of said stop being such t flight conditions withouttorque applied tor hub said stop remains in engagement, but hat uponapplication of a driving torque to the rotor hub, the blade lags aboutsaid pivot 6. In an aircraft sustaining rotor having a hub and a blade,pivot means articulating the blade to the hub including a pivot whoseaxis is inclined. upwardly and outwardly with respect to theloagitudinal blade axis to provide for decrease of blade pitch uponlagging movements thereof and increaseof blade pitch upon leadingmovements, the axis of said pivot passing a line joining the center ofgravity of the blade and the axis of the hub in a forwardly offsetposition with respect thereto when the blade is in true radial position.

7. In an aircraft sustaining rotor having a hub and a blade, pivot meansfor articulating the blade to the hub including two pivots both angledblade pitch upon movements thereof in the lagging direction and increaseof blade pitch upon movements from a lagging position, and said onepivot axis passing a line joining the center of gravity of the blade andthe axis of the hub in a forwardly ofl'set position with respect theretowhen the blade is in true radial position.

8. In an aircraft sustaining rotor having a hub and a blade, pivot meansfor articulating the blade to the hub including two pivots both angledwith respect to a plane perpendicular to the hub axis, the axis of oneof said pivots being inclined upwardly and outwardly with respect to thelongitudinal blade axis to provide for decrease of blade pitch uponmovements thereof in the lagging direction and increase of blade pitchupon gravity of the blade and the axis of the hub in a forwardly offsetposition with respect theretowhen the blade is in true radial position,the position of said one pivot axis and of the stop being such thatunder all normal flight conditions said stop remains in engagement butthat upon application of a driving torque to the rotor hub, the bladelags about said one pivot axis.

9. In an aircraft sustaining rotor having a hub and a blade, pivot meansarticulating the blade to the hub comprising a pivot having its axisangled with respect to a plane perpendicular to the axis of the hub andpassing a line joining the center of gravity of the blade and the axisof the hub in a forwardly offset position with respect thereto when theblade isin true radial position, and a releasable latch device forretaining the blade'in true radial position about said pivot.

10. In an aircraft sustaining rotor having a hub and a blade, a pivotjoining the blade with the hub and havingits axis obliquely inclinedwith respect to the longitudinal blade axis to provide for pitch changemovements of the blade upon displacements thereof in lagging and leadingdirections, the axis of said pivot passing-a line joining the center ofgravity of the blade and the hub axis in horizontally ofl'set relationwith respect thereto, means for applying a driving torque to the rotor,and means for holding the blade in low pitch position on said pivot axisduring application of the drive.

11. In an aircraft sustaining rotor having a hub and a blade, a pivotjoining the blade with the hub and having its axis obliquely inclinedwith respect to the longitudinal blade axis to provide for pitch changemovements of the blade upon displacements thereof in lagging and leadingdirections, the axis of said pivot passing a line joining the center ofgravity of the 'blade and the hub axis in horizontally offset relationwith respect thereto, means for applying a driving torque to the rotor,and mechanism for controlling the pitch position of the blade includingmeans for holding the blade in low pitch position about said pivot axis.during application of the drive and means for holding the blade inhigher pitch position on said pivot axis in flight blade duringautorotative flight operation, drive means for the rotor, a pivot havingits axis obliquely angled with respect to the longitudinal blade axisand providing for pitch change movements of the blade upon applicationof the driving torque to the rotor, the axis of the second pivot beingforwardly offset from the longitudinal blade axis.

13. In a bladed aircraft sustaining rotor capabio of autorotativeactuation in flight, mechanism for mounting the blade on a rotative hubincluding a pivot providing freedom for lag and lead displacements underthe influence of normal flight forces and a pitch change pivotautomatically operative to change the blade pitch under the influence ofthe application of a driving torque to the rotor, movement of the bladeabout the pitch change pivot being restrained during autorotationalactuation of the rotor by the action of centrifugal force on the bladein the absence of a driving torque, the axis of said pitch change pivotbeing horizontally offset from a line joining this center of gravity ofthe blade and the hub a 14. In an aircraft having an autorotationallyactuable sustaining rotor incorporating a hub and a blade, and mechanism'for driving the rotor, pivot means for connecting the blade with thehub including a pivot providing for pitch change movements of the bladewithin a range limited on the one hand by the substantially zero pitchposition of the blade, and on the other hand by a pitch positionsubstantially higher than the normal autorotational value, said pivotmeans providing for movement of the blade to the substantially zeropitch position automatically upon application of the driving torque tothe rotor and for movement of the blade to the pitch position higherthan the normal autorotational value upon cessation of driving torque ata rate of rotation higher than the normal autorotational rate, and meansurging the blade to move on said pitch change pivot from its higher thannormal autorotational pitch position to said autorotational pitchposition and providing for such pitch change movement upon reduction inspeed of rotation from a higher than normal rate to the normalautorotational rate.

15. In an aircraft having an autorotationally actuable sustaining rotorincorporating a hub and a blade, and mechanism for driving the rotor,pivot means for connecting the blade with .the hub including a pivotproviding for pitch change movements of the blade within a range limitedon the one hand by the substantially zero pitch position of the blade,and on the other hand by pitch position substantially higher than thenormal autorotational value, said pivot means providing for movement ofthe blade to the substantially zero pitch position automatically uponapplication of the driving torque to the rotor, and for movement of theblade to the pitch position higher than the normal autorotational valueupon cessation of driving torque at a rate of rotation higher than thenormal autorotational rate, means urging the blade to move on said pitchchange pivot from its higher than normal autorotational pitch positionto said autorotational pitch position and providing for such pitchchange movement upon reduction in speed of rotation from a higher thannormal rate to the normal autorotational rate, and a releasable latchdevice for retaining the blade in the autorota-.

tional pitch position.

16. In an aircraft having an autorotationally actuable sustaining rotorincorporating a hub and a blade, and mechanism for driving the. rotor, apivot means 'ior connecting the blade with the hub including a pivotproviding for pitch change movements of the blade within a range limitedon the one hand by the substantially zero pitch position of the blade,and on the other hand by pitch position substantially higher than thenormal autorotational value, said pivot means providing for movement ofthe blade to the substantially zero pitch position upon application ofthe driving torque to the rotor, and for movement of the blade to thepitch position higher than the normal autorotational value uponcessation of driving torque at a rate of rotation higher than the normalautorotational rate, means urging the blade to move on said pitch changepivot from its higher than normal autorotational pitch position to saidautorotational pitch position and providing for such pitch changemovement upon reduction in speed of rotation from a higher than normalrate to the normal autorotational rate, and a releasable latch devicefor locking the blade in the substantially zero pitch position.

17. For an aircraft, an autorotatable sustaining rotor having a hub anda blade, pivot mechanism mounting the blade on the hub including a pivotwhose axis is oblique to the longitudinal axis of the blade whereby toeffect blade pitch variation when the rotor is power driven, and

means positively rendering said pivot ineflective to vary the bladepitch during normal autorotational flight operation 01 the rotor.

18. In an aircraft sustaining rotor. a generally upright hub, agenerally radially extending blade, and pivot mechanism mounting saidblade on said hub comprising a pivot axis providing for generally up anddown flapping movements of the blade, a pivot axis radially oilfset fromthe hub axis and providing for blade movements generally forwardly andrearwardiy in the rotative path, and a pivot axis at an angle to a planeperpendicular to the hub axis and offset from a line perpendicular tothe hub axis and intersecting the second named pivot axis.

19. In an aircraft sustaining rotor, a generally upright hub, agenerally radially extending blade, and pivot mechanism mounting saidblade on said hub comprising a pivot axis providing for generally up anddown flapping movements of the blade, a pivot axis radially offset fromthe hub axis and providing for blade movements generally i'orwardly andrearwardly in the rotative path, and a pivot axis extending obliquely toa plane perpendicular to the hub axis in a sense providing for pitchvariation of the blade and horizontally oifset from a line perpendicularto the hub axis and intersecting the second named pivot axis.

HARRIS S. CAMPBEIL.

